Air separation employing separated nitrogen as heat exchange fluid in liquid oxygen pump jacket



June 1969 G. M. BASIN ETAL 3,447,332

AIR SEPARATION EMPLOYING SEPARATED NITROGEN AS HEAT EXCHANGE FLUID IN LIQUID OXYGEN PUMP JACKET Filed July 13, 1967 AdSORBER :T: :I: X 1i g I 1 5] a r I 2/ A 7 23 I I5 [32 I A F I5 20 1 X J V 1 8 PUMP I EXPAMDER It V v v [y AIR United States Patent CI. 62-13 1 Claim ABSTRACT OF THE DISCLOSURE Impurities are adsorbed from compressed air after WhlCh the air is split into three portions. First and second portions of air are cooled by separated air fractlons, recombined and then throttled while the third portion of air is cooled by separated air fraction, work expanded and then combined with the throttled air and introduced into a rectification column. Liquid oxygen from the column is heat exchanged with gaseous nitrogen exiting the column after which the oxygen is pressurized in a jacketed oxygen pump. A portion of the nitrogen from the oxygen heat exchange passes through the pump jacket after which the nitrogen is used to regenerate the absorber.

This invention relates to methods of producing oxygen from air by low-temperature rectification in a med umpressure cycle, comprising expanding a part of the an m an expander, pumping of the liquid oxygen to a heat exchanger where it is gasified, utilizing a part of the nitrogenleaving the rectification column for the regeneration of the purification unit adsorbent.

The most widespread of the prior art methods of producing oxygen from air are those involving air fractionation at low temperatures by rectification.

According to a known method, air is compressed to 45 to 55 abs. atm., freed of moisture and carbon dioxide, cooled in a heat exchanger by the outgoing fractionation products from the rectification column, which are mtrogen and oxygen.

A part of the air cooled in the heat exchanger to minus 100 C. is expanded in the expander.

The other part of the air cooled in the heat exchanger is expanded in a throttle valve and mixed with the air leaving the expander. The resulting vapor-liquid mixture passes to the rectification column for fractionation.

Fractionation of the air in the rectification column results in nitrogen and oxygen.

The nitrogen is utilized for cooling the liquid oxygen pump and is then fed to a heat exchanger where the nitrogen and the oxygen cool the incoming flow of initial compressed air.

After the heat exchanger, the nitrogen is divided into two parts, one of which, smaller in volume, is used for regenerating the purification unit adsorbent, and the other, larger in volume, passes through the nitrogenwater cooler, where it cools the initial compressed air, and thence to the atmosphere.

The liquid oxygen is fed to the liquid oxygen pump, gasified in the heat exchanger and passed to the consumer.

To insure normal operation of the purification unit the gauge pressure of the nitrogen before entering the purification unit should be 0.1-0.2 atm.

To obtain that nitrogen pressure, all resistances in the nitrogen line beyond the rectification column should be r 3,447,332, c Patented June 3, 1969 minimized. This is achieved by reducing the rate of flow of the nitrogen through the heat exchanger, but also entails such disadvantages as an increase in the heat exchange surface area, the dimensions and the weight of the heat exchanger.

Another disadvantage of said method is that by dividing the nitrogen into two streams after the heat exchanger, the greater part thereof is discharged to the atmosphere with its excess pressure unutilized.

It is an object of this invention to provide an economical process for producing oxygen from air.

It is another object of the invention to intensify the heat exchange between the initial air and fractionation products.

It is a further object of this invention to reduce the amount of metal and labor consumed in manufacturing the heat exchanging equipment.

Said objects have been accomplished by producing oxygen from air by the low-temperature rectification of air in a medium-pressure cycle wherein compressed air, preliminarily cooled and freed of moisture and carbon dioxide, is subjected to heat exchange with the outgoing fractionation products, and after expanding a portion of the air and throttling the rest, the two portions are mixed and sent to a rectification column for fractionation with subsequent removal of oxygen and nitrogen.

According to the invention, part of the total flow of nitrogen leaving the rectification column is removed from the section between said column and the point of entry of the nitrogen into heat exchange with the air.

The removed part is diverted to a heat exchanger in which said nitrogen exchanges heat with part of the initial air and the oxygen produced, after which it is used for the regeneration of the purification unit adsorbent.

The rest of the outgoing nitrogen is utilized for cooling another portion of the initial compressed air.

This invention possesses the following advantages over the prior art method described hereinabove: it enables utilization of the excess pressure of the rectification column for overcoming all resistances in the outgoing nitrogen lines and provides normal conditions for operation of the purification unit without requiring any additional expenditures.

By regulating the amount of nitrogen diverted to the adsorption step the pressure in both flows of nitrogen is varied within a preset range, making .it possible to use from 12 to 25% of the nitrogen for the regeneration of the purification unit adsorbent under the required gauge pressure and to pass the remaining to 88% of the nitrogen through the double-flow (air-nitrogen) heat exchanger at a lower pressure.

Such distribution of the flows of the outgoing nitrogen enables installment of small-size heat exchangers with intensive heat exchange.

For example, in the case of a medium-pressure unit with a compressed oxygen output of 400 m. /hr., the use of the present invention enables a reduction in the consumption of non-ferrous metals of up to 800 kg.

By thus lowering the cost of the heat exchanging equipment the present method provides a cost reduction in production per cubic meter of oxygen.

Hereinafter the invention is explained by a description of one embodiment of the method of producing oxygen from air with reference to the accompanying drawing which diagrammatically shows the production process.

Compressed air to be fractionated flows via conduit 1 to nitrogen-water cooler 2, where it is cooled, and thence via conduit 3 to adsorption purification unit 4 where the air is freed of carbon dioxide and moisture. From adsorption purification unit 4, the air passes via conduit 5 to heat exchangers 6 and 7.

In heat exchanger 6, the air is cooled by a counterfiow of nitrogen, while in heat exchanger 7, the air is cooled by counter-flows of nitrogen and oxygen.

Part of the air cooled preliminarily in heat exchanger 6 is expanded in expander 8 and then passes via conduit 9 to rectification column 10 for fractionation. The other part of the air passing through heat exchanger 6 and heat exchanger 7 through conduit 11, are expanded in throttle valve 12 and then also enter rectification column 10 for fractionation.

The nitrogen produced by the fractionation of air passes from rectification column 10 via conduit 13 to liquid oxygen supercoler 14 beyond which the greater portion of the nitrogen is diverted by regulating unit 15 via conduit 16 to heat exchanger 6 and, further, via conduit 17 to nitrogen-water cooler 2, and is thereafter expelled into the atmosphere.

The other part of the nitrogen, constituting a volume of from 12 to 25% passes via conduit 18 to the jacket of the liquid oxygen pump 19 for cooling the latter, and then via conduit 20 to heat exchanger 7 from which it flows via conduit 21 to purification unit 4 where it is used for regeneration of the adsorbent.

Liquid oxygen passes from rectification column 10 via conduit 22 through liquid oxygen supercooler 14, liquid oxygen pump 19, and is gasified in heat exchanger 7 and then fed in the gaseous state via conduit 23 to the consumer.

We claim:

1. A method of separating compressed air to produce gaseous oxygen and gaseous nitrogen, said method comprising freeing said compressed air of high-boiling impurities by adsorbing said impurities on an adsorbent, splitting the impurity free, compressed air into first, second and third portions, cooling the first of said air portions by heat exchange with the produced oxygen and gaseous nitrogen while cooling the second and third portions with produced gaseous nitrogen, subjecting the thus cooled third portion to work expansion, recombining the first portion of the air, after said heat exchange, with the second portion of the cooled air, throttling the thusly recombined first and second portions of the air, recombining the first, second and third air stream portions after expansion thereof and subjecting the combinedexpanded air to low-temperature rectification to obtain liquid oxygen and gaseous nitrogen, supercooling the liquid oxygen by heat exchange with the gaseous nitrogen from the rectification column, compressing the supercoled liquid oxygen in a pump whereby heat is evolied and abstracting the evolved heat by heat exchange with a part of the gaseous nitrogen which is directed, after heat exchange with the liquid oxygen, through the jacket of the pump, heating the compressed oxygen and the gaseous nitrogen from the pump jacket by heat exchange with the first portion of pressurized purified air to a temperature close to the temperature of the air after purification, and regenerating the adsorbent with said heated part of produced gaseous nitrogen after heat exchange with said first portion of pressurized air, wherein the nitrogen from the rectification column, after heat exchange with the liquid oxygen, is divided into two streams, a first of which is used for cooling the second and third portion of the air, and the second of whch is first passed through the jacket of the liquid oxygen pump and then directed, together with the compressed oxygen, to a heat exchanger for cooling the first portion of the pressurized air, followed by using the second nitrogen stream for regeneration of the adsorbent.

References Cited UNITED STATES PATENTS 2,915,882 12/1959 Schuftan et al 62-41 XR 2,955,434 10/1960 Cost 62-18 XR 2,968,160 1/196,1 Schilling et a1 62-1-8 XR 3,079,759 3/ 1963 Schilling.

3,086,371 4/1963 Schilling et al. 62-41 XR NORMAN Y-UDKOFF, Primary Examiner.

V. W. PRETKA, Assistant Examiner.

US. Cl. X.R. 6218, 38, 41 

